Fluid flow switch actuating mechanism



Dec. 8, 1959 A CROSKEY ET AL 2,916,576

FLUID FLOW SWITCH ACTUATING MECHANISM Filed Nov. 21. 1956 2 Sheets-Sheet l 54 INVENTOR S.

Z By 11w 22%? Dec. 8, 1959 F. A. CROSKEY ET 2,916,576

FLUID FLOW SWITCH ACTUATING MECHANISM Filed Nov. 21. 1956 2 Sheets-Sheet 2 IN VEN TORS.

United States Patent Ofiice 2,916,576 Patented Dec. 8, 1959 FLUID FLOW SWITCH ACTUATING MECHANISM Frank A. Croskey, New Baltimore, and Charles Derwood Tuttle, Wyandotte, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 21, 1956, Serial No. 623,729

1 Claim. (Cl. ZOO-81.9)

The invention relates to a full flow air actuated electrical switch and more particularly to the mechanism for actuating the switch when used in combination with electrostatic spray equipment.

In electrostatic spray painting of articles of manufacture, a spray gun is provided with air under pressure and paint is provided to the spray head supported by the gun. A charger head for elecrostatically charging the spray emitting from the nozzle of the spray head is charged'with a high voltage electric current. In order to control the current in conjunction with control of the spray mechanism it is desirable to provide a switch which is operable by air flow being supplied to the spray gun. In order to effectively control the electrostatic charge, the switch must operate satisfactorily within a wide range of air pressures and be unaffected by extreme pressures within the range. It must be sensitive to air flow rather than the pressure of the air, closing its contacts when there is any appreciable air flow and opening its contacts when air flow is stopped whether there is air pressure within the switch housing or not. The switch must allow relatively unrestricted air flow and have a long life with a minimum of maintenance. Switches previously available have not been operable without adjustment over the wide range of pressures found in spray painting equipment while having a long trouble-free life expectancy.

The switch embodying the invention is of the full flow type and is sensitive to air flow to the spray gun. There is no appreciable pressure drop. In order to protect the switch from paint vapors which may be present in the atmosphere, the switch is operated within a completely enclosed structure. It is also operated in a circuit having a low voltage and controls the high voltage charging circuit indirectly. This construction and arrangement decreases the likelihood of arcing within the switch. Even if arcing is present, the area in which it might take place is separated from any inflammable vapors which may be in the surrounding atmosphere.

In the drawings:

Figure 1 is a cross sectional view of an air flow switch embodying the invention and with the switch contacts open;

Figure 2 is a cross section view of a portion of the switch actuating mechanism as taken in direction of arrows 22 of Figure 1;

Figure 3 is a cross section view of a portion of the switch mechanism taken in the direction of arrows 3-3 of Figurel but with the switch contacts closed;

Figure 4 is a schematic view of the electrical power supply system for the electrostatic spray equipment and includes the circuits controlled by the switch of Figure 1.

As is shown in Figure l, the electrostatic spray mechanism includes a spray gun 12 having a trigger type control 14 for controlling the flow of air through the gun to the spray head 16 in which paint flowing through conduit 18 is mixed and sprayed from nozzle 20. An electrostatic charger head 22 is mounted adjacent spray nozzle 20 and passes an electrostatic charge to the paint particles emitted from the spray head. Air under pressure is delivered to the spray gun 12 through conduit 23.

The air flow switch embodying the invention is located in the air circuit leading to conduit 23 and is provided with an inlet port 24 and an outlet port 26 for connection into the air circuit. The switch proper which controls the low voltage circuit, thereby indirectly controlling the electrostatic charge, may be a micro switch 28.

The actuating mechanism for closing and opening the switch 28 is enclosed in a casing 30 in which inlet and outlet ports 24 and 26 are located. The casing is preferably cylindrical and its ends are closed by a base plate mounting member 32 and a cap 34. A pair of chambers is located within the casing. One of the chambers functions as an inlet chamber 36 while the other chamber 38 contains switch 28 and outlet port 26. Chambers 36 and 38 are seperated by a web 40 which may be integrally formed with casing 30. The web has a centrally located passage 42 extending therethrough which provides an air flow connection between chambers 36 and 38. A piston 44 may be reciprocably disposed within chamber 38 and provided with a stem 46 extending axially of the casing, passing through passage 42 and terminating within chamber 36. Piston 44 is also provided with a projection 48 on the opposite side of the piston from stem 46 which is adapted to contact button 50 of micro switch 28 through which the electrical contacts within the switch are actuated. A spring retainer 52 may be secured within chamber 36 and hold a relatively weak compression spring 54 which acts through retaining washer 56 on stem 46 to hold piston 44 lightly in contact with web 40 when there is no air flow through the casing 30. Piston 44 is also provided with an annular lip 58 extending from the stem side of the piston-and engageable with web 40 radially outward from passage 42, thereby sealing chamber 36 from chamber 38 when the lip is in contact with the web. The walls of chamber 38 are provided with a plurality of grooves 60 which extend from web 40 to cap 34. When piston 44 is moved away from web 40, air flow is allowed to pass from chamber 36 between lip 58 and web 40 and around piston 44 through the grooves 60.

Cap 34 may be provided with inwardly extending switch supports 62 and 64 to which switch 28 may be tween supports 62 and 64, the movement of piston 44 may be allowed to close the contact within switch 28 by pressing against button 50. A slightly additional movement of the piston brings it into engagement with switch supports 62 and 64, preventing further movement of the piston. By this arrangement the micro switch does not transmit the heavier loads resulting from increased air flow and higher pressure differentials. The range of presssures under which the unit is normally operated includes air pressures from 0.5 p.s.i. to p.s.i., and it may be even greater without injury to the unit or the necessity of making adjustments to permit such an operative latitude.

In operation, the switch actuating mechanism is in the position shown in Figure 1 when there is no air flow present through ports 24 and 26 to the spray mechanism 10. When the trigger 14 is actuated by the operator, opening a valve in the spray gun and allowing air to flow from conduit 23 to the spray head 16, air enters chamber 36 through port 24 and passes through passage 42, which is sufiiciently larger than stem 46 to allow free passage of air between the web 40 and the stem, acting against the lower side of piston 44 and moving the piston upwardly. The air then passes between web 40 and lip 58 into grooves 60 and chamber 38. Outlet port 26 connects chamber 38 with conduit 23. When piston 44 is moved upwardly projection 48 contacts button 50 of micro switch 28. As the piston continues to move upwardly the contacts within switch 28 are closed. A slight additional upward movement of piston 44 engages switch support 62, and 64 with the upper side of piston 44, stopping the upward movement of the piston. Any add1- tional. force exerted upwardly on piston 44 is bypassed around switch 28 through the supports 62 and 64 to cap 34. The switch itself is therefore not required to resist the full forces exerted on piston 44 but it is only required to allow sufiicient movement of the piston to close the switch contacts. As long as air continues to flow through the actuating mechanism, piston 44 remains in its upward position as shown in Figure 3 and is unaffected by pressure variations within the air system. When air flow is shut 01f by release of the trigger control 14, piston 44 returns into engagement with web 40 since there is no air fiow within the actuating mechanism. Lip 58 again contacts web 40 and chambers 36 and 38 are again sealed from each other.

The power supply system shown schematically in Figure 4 is furnished with an alternating voltage from an appropriate source such as the conventional power supply line of 110 volts through plug 66. This voltage energizes rectifier 68 to develop a high direct voltage power output. This power output is supplied through filter 70 to develop the plate supply voltage for the push-pull type oscillator 72. The oscillator output voltage is transformer coupled to the rectifier and booster section 74 to develop the high direct voltage power which is supplied to the charging head for the electrostatic sprayer through jack plug 76.

The transformer secondary winding 78 has a low alternating voltage induced therein for supplying the oscillator tube heater circuits. The oscillator cathode circuit is returned to ground through relay 80 and is connected to that relay at contacts 6 and 8. The air-flow switch circuit 82 controls relay 80 through a low alternating voltage circuit which includes relay coil 84. The switch 28 is actuated by the mechanism described above. A double pole single throw switch 86 may be provided for manual control and is located in the cathode ground circuit 88. A pilot signal light 90 may be furnished in low alternating voltage circuit 92 which is in parallel with the air-flow switch 28 and in series with the manual air-fiow switch 86. When either of these switches is closed, the signal light is energized and indicates that an operative condition is in existence in the power supply system. A pilot light 94 may be positioned in the oscillator cathode heater circuits to indicate energization of that circuit. A meter jack 96 may be provded to obtain desired meter readings in the charger head circuit.

By locating switch 28 within the air flow circuit, the switch is sealed from the atmosphere surrounding the switch actuating mechanism and is located in an air stream having no inflammable vapors such as are common with paint spray mechanisms. This location of the switch eliminates a fire hazard by sealing any possible switch arcing from paint vapors that might be present. By placing switch 28 within a low voltage circuit and indirectly controlling the high voltage required for the electrostatic charger head, the possibility of arcing within the switch is substantially reduced. Previous switches which have been actuated concurrently with the air by movement of the trigger control 14 have required that Wires in the switch circuit extend to the spray gun adjacent the trigger in order that the circuit be closed and opened by movement of the trigger. These wires created an additional maintenance problem as well as electrical hazards and operating inconveniences. The switch herein disclosed allows the electrostatic charging circuit control to be placed anywhere along the air supply system. It will operate as well at the end of the air supply hose remote from the spray gun as next to the gun, and therefore may be more safely located both in terms of electrical hazards and liability to injury from being handled constantly. The switch will also perform well in large volume automatic systems as well as in hand-controlled systems. It may also be advantageously employed in other systems requiring a fluid flow circuit controlling switch.

What is claimed is:

For use in an electrostatic spray mechanism having an air supply hose and a nozzle and a charger head, a switch actuated by air flow in said hose for controlling the electrical power supply to said charger head, said switch comprising a case having an inlet and an outlet port and an inlet chamber and a switch chamber, a web in said case separting said chambers and having a passage formed therein, said switch chamber having an elec-, trical switch disposed therein, a piston disposed for reciprocation in said case and having a piston head and a stem extending through said passage, said piston head being positioned in said switch chamber and having an annular lip formed on one side thereof, said lip extending around said passage and adapted to contact said web to seal said passage, a plurality of grooves in said switch chamber walls having a combined cross section area at least equal to the area of said passage around said stem whereby unrestricted air may flow around said piston when said piston lip is out of contact with said web, the air mass flow admitted through said inlet port moving said piston away from said web, said piston engaging said electrical switch whereby said power supply is energized.

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